Field of the Invention
The present invention relates to a method and apparatus for manufacturing a single crystal using the Czochralski method (CZ method) and, more particularly, to a method and apparatus that inspects abnormality of a luminance distribution of an image taken by a camera that photographs the inside of a chamber and corrects the abnormality.
Description of Related Art
Many silicon single crystals used as a material for silicon wafers are manufactured by the CZ method. In the CZ method, a seed crystal is dipped into a silicon melt contained in a quartz crucible and slowly pulled up while rotating the seed crystal and crucible to grow a silicon single crystal with a large diameter at a lower end of the seed crystal.
In order to improve silicon wafer yield, it is important to suppress fluctuations in the diameter of a single crystal. As a method of controlling the diameter of a single crystal constant, there is known a method that measures the diameter of a single crystal being pulled up and controls pull-up conditions based on the measuring result so as to make the diameter of the single crystal constant. For example, Japanese Patent Application Laid-Open No. 2003-12395 describes a method that photographs an image of a boundary between a single crystal and melt using a camera, measures a diameter and a center position of the single crystal from the photographed image, and controls power of a heater and operations of a pull-up apparatus based on the measurement result.
Further, Japanese Patent Application Laid-Open No. 1986-122188 describes a method that detects a single crystal, a melt surface, and a fusion ring generated between the single crystal and the melt surface by using a linear image sensor. Further, Japanese Examined Patent Application Publication No. 1993-049635 describes a method that detects a position of a fusion ring by an optical sensor and measures a diameter of a single crystal based on the detection result. More specifically, in this method, a light shielding plate is disposed between a peripheral wall of a crucible and a single crystal to be pulled up so as to eliminate optical influence from the crucible, whereby a diameter measurement error is reduced.
As described above, in the single crystal diameter measurement, the inside of a chamber is photographed by a camera, and the single crystal diameter is calculated from an image of the fusion ring generated at the boundary between the single crystal and the melt. The inside of the chamber is photographed through an observation window provided at an upper portion of the chamber.
However, an SiO gas is generated by silicon melt evaporation inside the chamber during a pull-up process of the single crystal, and a glass surface of the observation window is clouded by influence of the SiO gas, which may result in unevenness in the luminance distribution of the photographed image. In order to cope with this, an argon gas (purge gas) is introduced into the chamber, and the SiO gas generated inside the chamber is discharged outside the chamber together with the argon gas. However, the SiO gas inside the chamber cannot completely be removed, so that it is difficult to completely prevent adhesion of the SiO gas to the glass surface of the observation window. When SiO unevenly adheres to the glass surface of the observation window due to long-term continuous use of the chamber to increase unevenness in a luminance distribution in a horizontal axis direction of the photographed image, the diameter of the silicon single crystal may be erroneously measured, causing fluctuations in single crystal diameter.